The present invention relates to polypropylene resin compositions to be used for injection molding and moldings prepared therefrom.
Polypropylene is used very widely as a general purpose resin, since it is inexpensive and it has excellent properties. Recently, more excellent properties are required of housings and casings of domestic electric appliances in many cases. For example, polypropylene of a grade which satisfies all properties of gloss, impact strength and rigidity cannot be obtained. In other words, a polypropylene having excellent gloss an impact strength has low rigidity, another polypropylene having excellent gloss and rigidity has a low impact strength and still another polypropylene having high impact strength and rigidity has poor gloss. Under the circumstances as above, a process for improving impact strength of a polypropylene of excellent gloss and rigidity by blending it with ethylene/propylene rubber was reported in Kunio Goto's "Polymer Blend", pages 168-180, published on Nov. 21, 1970. However, this process has a defect that tensile strength, bending strength and particularly rigidity and gloss and reduced seriously. There has been a study on improvement in rigidity of ethylene/propylene copolymer by incorporating an inorganic filler in an ethylene/propylene copolymer of excellent gloss and impact strength. However, this method is accompanied with a practical problem, since the gloss and impact strength are reduced by the incorporation of the powdery inorganic filler. In addition, in this method, a considerable amount of the inorganic filler is required for improving rigidity, which causes a significant reduction in tensile strength, bending strength and moldability, in addition to said reduction in gloss and impact resistance, unfavorably.
After all, there is no method of improving all of the three properties of gloss, rigidity and impact strength heretofore.